A Palestinian woman and four children have died in an explosion near a Gaza refugee camp as US Middle East envoy Anthony Zinni pursued his latest peace mission.

Palestinian officials said the woman, her three children and a young nephew had been riding in a donkey cart near al-Bureij camp when they detonated a landmine left behind by withdrawing Israeli security forces.

As always, I'm optimistic. Despite the conditions, I think there
are the ingredients here for hope

US envoy Anthony Zinni

Israel has denied any responsibility, saying the explosion was caused by Palestinian militants.

Mr Zinni has been meeting Palestinian leader Yasser Arafat in Ramallah, following talks with Israeli ministers.

To coincide with his visit, Israeli forces withdrew from key areas in the West Bank and Gaza Strip that they had occupied in the army's biggest ground operation for 20 years.

The withdrawal brought praise from US President George W Bush who also said he was hopeful that Mr Zinni
would succeed in bringing about a ceasefire.

After his meeting with Mr Peres in Tel Aviv, Mr Zinni said: "As always, I'm optimistic. Despite the conditions, I think there
are the ingredients here for hope. So, I'm encouraged."

He then travelled to meet Mr Arafat who, according to one of the Palestinian leader's senior aides, was waiting with his
own ceasefire plan.

Israeli tanks withdrew from key areas

Israeli forces pulled back from Ramallah, Tulkarm, Qalqilya and parts of the Gaza Strip early on Friday, although reports said tanks remained close by.

The army remains in parts of Bethlehem and is still surrounding some other Palestinian areas.

Israel described the withdrawal as a goodwill gesture designed to help General Zinni's efforts.

More violence

Palestinians dismissed the moves as a political trick.

The US has been insisting on a complete withdrawal by Israel from all the Palestinian areas it has occupied over the past few days, as a precondition for ceasefire talks.

The Palestinian Authority has also said the Israelis should withdraw fully before they will hold talks.

Palestinian militants are vowing to keep up their attacks

But even as the talks got under way there were reports of more violence.

Palestinian security chiefs in Gaza said a landmine left behind by occupying forces caused the explosion that killed Zeina Awawdeh, 43, her son
Salem, eight, her daughters Dahani, 14, and Amaneh, 16 and a
nephew, Tareq, 12.

Two other children were also injured.

They described the explosion as a crime, committed by Israel against a mother and her children.

A spokesman for the Israeli defence forces told the BBC the Israeli army had nothing to do with the explosion.

They suggested the mine was a device left by Palestinian militants and meant to harm Israeli forces.

Earlier in Ramallah, eyewitnesses told the BBC that two Israeli armoured vehicles had been attacked and destroyed.

The Israeli army denied this, saying that none of its armoured vehicles had been hit.

It said that a car blew up killing two Palestinians on a road east of Ramallah.